Classical CDs Weekly: Beethoven, Mahler, Piaf, Poulenc

Beethoven: Diabelli Variations, Sonata no 32, Bagatelles András Schiff (piano and fortepiano) (ECM)

Invest in a copy of Jeremy Denk's zingy new Goldberg Variations and you'll hopefully be prompted to purchase this rather special András Schiff Beethoven disc – or discs, as he gives us two performances of the Diabelli Variations – one on a velvet-toned 1921 Bechstein once used by Wilhelm Backhaus, and the second on a Franz Brodmann fortepiano built a century earlier. Schiff asks us to wonder whether Beethoven would have liked the Steinway, suggesting that the composer's response might be “Why is this thing so black? It looks like a coffin! Why is the bass so ponderous...?” Beethoven would reluctantly conclude that only a modern instrument's sound can fill a huge concert venue – a tinkly fortepiano can easily become inaudible in a large hall. Schiff's Steinway performance is superbly entertaining – his Buster Keaton approach makes the jokes far subtler than they can be, and it's impossible to suppress giggles of incredulity at the music's odder excursions – right and left hands at odds in Variation 2, or the erratic bursts of energy which suddenly erupt, shattering any hint of pomposity. The final minuet steals on shyly, coyly, seemingly oblivious to what's gone before. Schiff also plays the Op.111 Sonata on the Steinway – its long second movement another extended set of variations.

The fortepiano performance on the second disc is yet more remarkable – subtly edgier, more extreme, the instrument sounding as if it's about to buckle under the strain. Beethoven's eccentric Six Bagatelles makes a magnificent coda, their strangeness accentuated by the fortepiano sound. ECM's presentation is fabulous – it's always enlightening to see reproductions of Beethoven's own musical handwriting, full of scratches, scribbles and smudges. Schiff's and Paul Griffith's notes are erudite and accessible, and it's a pleasant surprise to see a colour photograph on an ECM sleeve.

Mahler: Das Lied von der Erde Sarah Connolly (mezzo), Toby Spence (tenor), London Philharmonic Orchestra/Yannick Nézet-Séguin (LPO)

This live performance starts in a mood of bullish exuberance; horns blasting out their pentatonic fanfare with furious energy. You realise that it's something very special in the first song's rapt, quiet centre, the orchestra's principal trumpet magnificent in that tiny, crucial, solo. The orchestral playing is exceptionally good – every aching swell in tutti strings caught to perfection, and there's some exquisite solo woodwind playing. Das Lied von der Erde can be a bit of a slog, but Yannick Nézet-Séguin is alive to its wittier corners – Von der Jugend sounds here like a sophisticated offcut from The Mikado and the brassy romp in the middle of Von der Schönheit is riotous for all the right reasons. And vocally it's highly impressive; you sense that both Sarah Connolly and Toby Spence have put the work in during rehearsal and have shared their thoughts with Nézet-Séguin. Concert performances can be hard to balance, but Andrew Walton and Mike Clements achieve miracles here; Spence never sounds intimidated by the LPO playing at full pelt; his plaintive words at the close of the first song pack an incredible punch. He's great, in other words.

But any reading stands or falls on the quality of the mezzo-soprano. Connolly doesn't disappoint; the voice youthful, rich. Importantly, she's got superb diction. I can remember hearing a terrible Proms performance in the 1980s with an extremely starry soprano in her prime – despite my being near the front of the arena, the words completely failed to register. Der Abschied is paced to perfection here, its quieter corners tender, intimate and moving. Nézet-Séguin's funereal outbursts are suitably chilling, leading to one of the most glorious fadeouts imagineable. All caught in detailed, warm sound. I've long had a love/hate relationship with Das Lied; this team have made me swoon over the work again.

The Rascal and the Sparrow: Poulenc meets Piaf Antonio Pompa-Baldi (piano) (Steinway & Sons)

Here's some much-needed light relief. I'm currently wallowing in Hyperion's glorious box set of Poulenc's complete songs, to be reviewed here in a few weeks. As a stopgap, here's a delicious disc issued on Steinway & Sons' own label. There's no record of Poulenc and Edith Piaf ever having met, though they died in the same year (1963), and Poulenc dedicated one of his late piano works to the singer. Jody Hewgill's loveable sleeve art shows them arm in arm, and pianist Antonio Pompa-Baldi's justification for putting the two together is simply that “to me, they share some important traits, as musicians and human beings”. The musical links are easier to find; Poulenc's own songs are intensely melodic, their harmonies infused with the ambience of Parisian music hall. It helps that Pompa-Baldi's Poulenc transcriptions are so beautifully realised, as are Roberto Piana's subtle, sophisticated "elaborations" of numbers made famous by Piaf. The styles never clash.

Songs such as C and Nos souvenirs chantent are among the most beguilling of the Poulenc transcriptions. Yet more moving is a tender, understated version of Montparnasse. Vous n'écrivez plus? closes the anthology in high spirits. Understandably, texts aren't provided, so without the thick Hyperion booklet you'll be rushing to Google for the missing lyrics. There's also the bittersweet Improvisation in C minor, subtitled Hommage à Edith Piaf, sweetly dispatched by Pompa-Baldi. Piana's Piaf transcriptions are great fun. Hymne à l'amour takes on impressive weight, and Je ne regrette rien's sophisticated new clothes fit nicely. A treat, in other words.